The Sunday Nation
Nairobi,
16 June 2013
Kibet Kipkeu is wondering what a dimension is
and whether there are more than three dimensions. The answer is that it
depends on whom you ask: a scientist or a spiritualist. To the latter, I
think it refers to a world parallel to the one we exist in…if you can
comprehend what that means!
In geometry (a science), a dimension is simply
a basic direction of measuring length. It is “basic” because it cannot
be expressed by a simpler measure. Thus a one dimensional measurement is
a straight line.
A curve on a flat plane surface, say, a table
top, has two dimensions because its size can be defined by two
perpendicular straight lines – one running left to right (width) and the
other from back to front (length).
All other objects, be they chairs, stones,
buildings…and even planets are three dimensional. Their sizes can be
expressed using three basic measurements – width, length and height
(extent from bottom to top).
When you think about it; one- and
two-dimensional objects do not exist: lines, circles, triangle, squares
and the like are just pigments of our imagination! If I asked you to
give me a circle, you’d probably cut out a piece of paper in that shape.
But when you look at it closely, you will notice that it has a thickness
which is a height. Thus it is a very thin cylinder – a three dimensional
object.
In physics, a dimension has another meaning:
It is also a basic unit of measurement. That is, one that cannot be
expressed by a simpler unit. Coincidentally, there are also three,
namely, metres (for measuring lengths), kilograms (mass) and seconds
(time).
All other quantities are a combination of any
or all of these three. Thus speed in kilometres per hour breaks down to
the thousands of metres (1km = 1,000m) travelled after every 3,600
seconds. The same can be done to any measurable quantity, be it a force,
pressure, energy, power…anything!
But I suspect that Kibet was thinking about
the geometrical understanding of the term. The answer to the second part
of his question (whether there are more than three dimensions) is yes.
But we cannot observe the extra ones because we live in a three
dimensional world.
Nevertheless, the idea of time as the fourth
has been popularised in the public domain. But there is a challenge that
is normally ignored in popular discourse. This is the fact that time is
measure in seconds while the other geometrical dimensions (length, width
and height) are measured in metres.
The challenge then is this: isn’t grouping
metres and seconds together akin to mixing oranges and lemons? How many
lemons make one orange?
To overcome this hurdle, physicists figured
out that if time is multiplied by speed, the result is a distance. Since
distances are measured in metres, such a manipulation can resolve the
challenge. But which speed should be used?
The best choice must be one that is constant throughout the universe. And that turns out to be the speed of light. Thus strictly speaking, the fourth dimension is time multiplied by the speed of light.
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